Regenerated carbon black, mixture of regenerated carbon black and liquid polymer, rubber composition, and rubber product

Abstract

The problem addressed by the present invention is to provide: a regenerated carbon black capable of maintaining the physical properties of a rubber composition even when reused in the rubber composition; and a mixture of regenerated carbon black and a liquid polymer. This problem is solved by: a regenerated carbon black obtained by decomposing a crosslinked rubber containing a diene rubber and carbon black, said regenerated carbon black being characterized in that the content of organic components remaining in the regenerated carbon black after toluene washing is 5 mass% or more; and a mixture of regenerated carbon black and a liquid polymer, the mixture being characterized in that the weight average molecular weight of the liquid polymer is 300,000 or less.

Description

Technical Field

[0001] This disclosure relates to recycled carbon black, mixtures of recycled carbon black and liquid polymers, rubber compositions and rubber articles. Background Technology

[0002] Traditionally, rubber products, primarily composed of cross-linked rubber such as vulcanized rubber, are difficult to reuse and are often reused as fuel, particularly in cement plants, at the end of their product life. However, in recent years, with increasing awareness of environmental issues, there has been a need to develop methods for reusing materials obtained by decomposing rubber products rather than burning them as fuel.

[0003] Various methods exist for decomposing crosslinked rubber. For example, Patent Document 1 discloses the thermal decomposition of organic materials, such as waste tires, at 550°C to 800°C, and further discloses the use of carbon black obtained by thermal decomposition as a filler in rubber mixtures.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: EP 3427975 A1 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Typically, rubber products made from cross-linked rubber use rubber compositions containing diene rubber and fillers such as carbon black. Therefore, carbon black can be recovered as described in Patent Document 1 above by decomposing the cross-linked rubber. Furthermore, the inventors have discovered that by selecting the decomposition conditions of the cross-linked rubber, not only carbon black can be obtained, but also the constituent monomers and oligomers (liquid polymers) of the diene rubber can be obtained.

[0009] However, when recycled carbon black obtained through the decomposition of crosslinked rubber is reused in rubber compositions, the problem is that the physical properties of the resulting rubber compositions deteriorate.

[0010] Therefore, this disclosure solves the problem of providing recycled carbon black that can maintain the physical properties of rubber compositions even when reused in rubber compositions.

[0011] Furthermore, this disclosure also addresses the problem of providing mixtures of such recycled carbon black and liquid polymers, as well as rubber compositions and rubber articles containing such recycled carbon black.

[0012] Solution for solving the problem

[0013] The present disclosure for solving the above problems comprises the following essential components: recycled carbon black, mixtures of recycled carbon black and liquid polymers, rubber compositions, and rubber articles.

[0014] [1] A recycled carbon black, which is obtained by decomposing a crosslinked rubber comprising diene rubber and carbon black, wherein

[0015] The residual organic components in the recycled carbon black after toluene washing are more than 5% by mass.

[0016] [2] According to the recycled carbon black in [1], its maximum DTG temperature is above 350°C, where the maximum DTG temperature is the temperature at which the DTA value is at its maximum during thermogravimetric analysis, accompanied by the weight loss of organic components.

[0017] [3] A mixture of recycled carbon black and a liquid polymer, obtained by the decomposition of a crosslinked rubber comprising diene rubber and carbon black, wherein

[0018] The recycled carbon black is recycled carbon black according to [1] (in other words, recycled carbon black in which the organic component remaining in the recycled carbon black after toluene washing is more than 5% by mass) or recycled carbon black according to [2].

[0019] The liquid polymer has a weight-average molecular weight of less than 300,000.

[0020] [4] A mixture of recycled carbon black and a liquid polymer, obtained by the decomposition of a crosslinked rubber comprising diene rubber and carbon black, wherein

[0021] The recycled carbon black is recycled carbon black according to [1] (in other words, recycled carbon black in which the organic component remaining in the recycled carbon black after toluene washing is more than 5% by mass) or recycled carbon black according to [2].

[0022] The proportion of components with a molecular weight of less than 15,000 in the liquid polymer is less than 30% by mass.

[0023] [5] A rubber composition comprising a rubber component and recycled carbon black according to [1] or [2].

[0024] [6] A rubber composition comprising a rubber component and a mixture of recycled carbon black and a liquid polymer according to [3].

[0025] [7] A rubber composition comprising a rubber component and a mixture of recycled carbon black and a liquid polymer according to [4].

[0026] [8] A rubber composition according to any one of [5] to [7], wherein the rubber composition is used for a tire.

[0027] [9] A rubber article comprising a rubber component made of a rubber composition according to any one of [5] to [7].

[0028]

[10] The rubber product according to [9], wherein the rubber product is a tire.

[0029] The effects of the invention

[0030] According to this disclosure, recycled carbon black can be provided that retains the physical properties of the rubber composition even when reused in a rubber composition.

[0031] Furthermore, according to this disclosure, mixtures of such recycled carbon black and liquid polymers, as well as rubber compositions and rubber articles comprising such recycled carbon black, can be provided. Attached Figure Description

[0032] In the attached diagram:

[0033] Figure 1 A graph illustrating the relationship between temperature and DTG value [μg / min] of the recycled carbon black used in Example 1 and Comparative Examples 1 and 2, as well as the recycled carbon black mainly used in Example 2.

[0034] Figure 2 A graph illustrating the relationship between temperature and DTG value (DTG / maximum DTG[%]) of the recycled carbon black used in Example 1 and Comparative Examples 1 and 2, and the recycled carbon black mainly used in Example 2. Detailed Implementation

[0035] In the following, the recycled carbon black, mixtures of recycled carbon black and liquid polymers, rubber compositions and rubber articles of the present disclosure will be illustrated and described in detail with reference to their embodiments.

[0036] <Definition>

[0037] The compounds described in this specification may be derived in whole or in part from fossil resources, from biological resources such as plant resources, or from renewable resources such as waste tires. Furthermore, they may be derived from any mixture of two or more of fossil resources, biological resources, and renewable resources.

[0038] <Recycled Carbon Black>

[0039] The recycled carbon black of this embodiment is obtained by decomposing a cross-linked rubber comprising diene rubber and carbon black. The recycled carbon black of this embodiment is characterized in that the residual organic components in the recycled carbon black after toluene washing are 5% by mass or more.

[0040] As described above, when recycled carbon black obtained through the decomposition of crosslinked rubber is reused in rubber compositions, the physical properties of the resulting rubber composition are reduced. The inventors of this disclosure have conducted in-depth research and discovered that conventional recycled carbon black contains only a small amount (at most about 4% by mass) of organic components, while by reusing recycled carbon black containing 5% or more of organic components in rubber compositions, the physical properties of the resulting rubber composition, such as tensile strength (TB) and elongation at break (EB), can be maintained. While not wishing to be bound by theory, it is believed that the recycled carbon black of this embodiment improves dispersibility in the rubber components of the rubber composition by containing 5% or more of organic components, thereby maintaining the physical properties of the rubber composition.

[0041] (Organic components)

[0042] The recycled carbon black of this embodiment is obtained by removing liquid polymer components and low molecular weight organic compounds from a mixture containing liquid polymer and recycled carbon black obtained by decomposing a crosslinked rubber containing diene rubber and carbon black using toluene as a washing solvent. The recycled carbon black obtained thereby has a residual organic component of 5% by mass or more, preferably 10% by mass or more, and more preferably 30% by mass or less. If the organic component of the recycled carbon black is less than 5% by mass, the physical properties of the resulting rubber composition decrease when reused in a rubber composition. 50% by mass or more of the organic component is a diene polymer, preferably 80% by mass or more, and more preferably 90% by mass or more.

[0043] It should be noted that in this specification, the "organic component" of the recycled carbon black is measured by thermogravimetric analysis (TGA) as the difference between the mass (m0) of the tested recycled carbon black after heating it to 120°C and holding it for 1 hour and the mass (m1) after subsequently heating it to 550°C and holding it for 2 hours, calculated according to the following formula:

[0044] Organic component (mass %) = (m0 - m1) / m0 × 100

[0045] Therefore, in this specification, the "organic component" of recycled carbon black can also be referred to as the difference (weight loss) between the mass at 120°C and the mass at 550°C. It is assumed that the organic component mainly exists on the surface of the recycled carbon black.

[0046] (Maximum DTG temperature)

[0047] The maximum DTG temperature (the temperature at which the DTA value associated with the maximum weight loss of organic components in thermogravimetric analysis) of the recycled carbon black in this embodiment is preferably 350°C or higher. The DTG (Differential Thermogravimetric Analysis) curve is the first derivative curve of the TG (Thermogravimetric Analysis) curve, and the maximum DTG temperature corresponds to the temperature at which the weight loss of organic components is fastest. Recycled carbon black with a maximum DTG temperature of 350°C or higher has a high proportion of organic components remaining at high temperatures above 350°C and exhibits high dispersibility in rubber components, thus ensuring more reliable maintenance of the physical properties of the resulting rubber composition even when reused in rubber compositions.

[0048] (Dispersion stability)

[0049] In this embodiment, the dispersion stability of the recycled carbon black in toluene is 0.5 or higher. When the dispersion stability of the recycled carbon black in toluene is 0.5 or higher, the physical properties of the resulting rubber composition can be maintained more reliably when the recycled carbon black is reused in the rubber composition.

[0050] It should be noted that the product "LUMiSizer" can be used. ® The "Dispersion Stability of Recycled Carbon Black in Toluene" (LUM GmbH -611) method (LUMiSizer is a registered trademark in Japan, other countries, or both) measures the dispersion stability of recycled carbon black in toluene. The test carbon black or recycled carbon black was dispersed in toluene for 30 minutes to a concentration of 5 wt% using an ultrasonic cleaner at 120 W output and 40 kHz frequency. After dispersion, the dispersion was placed in a polyamide sample tube with a transmission section thickness of 2 mm and further dispersed for 5 minutes in an ultrasonic cleaner at 120 W output and 38 kHz frequency. Transmittance was then analyzed using a light source at a wavelength of 865 nm in 6x sensitivity mode. The rate of change of transmittance over time was calculated by measuring the transmittance at device positions from 110 mm to 125 mm at a constant rotation speed, and the reciprocal of this value was used as the dispersion stability to determine the dispersion stability in toluene. A higher dispersion stability value indicates higher dispersion stability in toluene.

[0051] (Proportion of clustered blocks)

[0052] In this embodiment, the recycled carbon black preferably has a particle size distribution of 5 μm or more, as measured by a particle size distribution measuring device, with a proportion of 50% by volume or less, when the recycled carbon black is ultrasonically dispersed in toluene solvent. When reused in rubber compositions, recycled carbon black with a proportion of 50% by volume or less of aggregates with a diameter of 5 μm or more can more reliably maintain the physical properties of the resulting rubber composition.

[0053] Furthermore, in this embodiment, the recycled carbon black preferably has a particle size distribution of 50% or more, as measured by a particle size distribution measuring device, where the recycled carbon black is dispersed ultrasonically in toluene solvent. When reused in a rubber composition, recycled carbon black with a particle size distribution of 50% or more, where the recycled carbon black has a particle size distribution of 1μm or less, can more reliably maintain the physical properties of the resulting rubber composition.

[0054] The proportion of aggregates with a diameter of 5 μm or more and the proportion of aggregates with a diameter of less than 1 μm in recycled carbon black can be measured by the following methods.

[0055] A dispersion of the test recycled carbon black in toluene solvent was prepared at the optimal concentration (0.1-5 wt%) and dispersed for 5-30 minutes using an ultrasonic cleaner at 120 W output and 40 kHz frequency. Using a Mastersizer 3000 and Hydro SV (manufactured by Malvern Panalytical), toluene was filled into the Hydro SV tank at room temperature as a solvent, and the toluene dispersion of the test recycled carbon black was added while stirring at 500-1000 rpm until the scattering intensity reached 10-20%. The test recycled carbon black was processed into non-spherical particles with a refractive index of 1.746, and the refractive index of toluene was set to 1.49. The particle size distribution was measured. Based on the obtained particle size distribution curve, the proportion of aggregates with a diameter greater than 5 μm and the proportion of aggregates with a diameter less than 1 μm were determined.

[0056] (Sulfur component and zinc component)

[0057] The recycled carbon black of this embodiment preferably has sulfur and zinc components adhering to its surface. Such recycled carbon black can be obtained without washing or surface treatment of the carbon black.

[0058] Whether sulfur and / or zinc components are attached to the surface of recycled carbon black can be confirmed by transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) without any treatment to remove inorganic substances, such as separation, washing or surface treatment of products obtained by pyrolysis.

[0059] (Cross-linked rubber)

[0060] The crosslinked rubber used as a raw material for the recycled carbon black of this embodiment comprises diene rubber and carbon black, and may further comprise other components. The recycled carbon black of this embodiment is obtained by decomposing such crosslinked rubber.

[0061] The crosslinked rubbers used for decomposition can be pre-grouped by the type of diene rubbers in the blend, and each group can be decomposed. Alternatively, they can be pre-grouped by the type of filler in the blend (e.g., type of carbon black, type of silica, mixing ratio of carbon black and silica, etc.), and each group can be decomposed. Furthermore, grouping can be performed by diene rubber type and by filler type, and each group can be decomposed. When each group is decomposed in this manner, liquid polymers, recycled carbon black, recycled silica, etc., with more uniform properties can be obtained, and when re-blended into a rubber composition, a rubber composition with better properties can be obtained.

[0062] Furthermore, when the crosslinked rubber used for decomposition is derived from tires, it can be pre-grouped by tire type (e.g., for passenger cars, for trucks and buses, for large vehicles such as off-road vehicles, for aircraft, for agricultural vehicles, etc.), and each group can be decomposed. Alternatively, it can be pre-grouped by tire components (e.g., tread rubber, sidewall rubber, bead portion rubber, steel cord coated rubber, organic fiber coated rubber, liner rubber, cushion rubber, etc.), and each group can be decomposed. Furthermore, grouping can be performed by tire type and by tire component, and each group can be decomposed. When each group is decomposed in this manner, a liquid polymer or recycled carbon black with more uniform properties can be obtained, and when re-blended into a rubber composition, a rubber composition with better performance can be obtained.

[0063] There are no particular limitations on the form of cross-linked rubber, and it can be, for example, powdered rubber. Such powdered rubber can be obtained by cutting and shredding used rubber products, such as waste tires. The shredding process can include multiple steps, such as a preliminary shredding step and a fine shredding step, and after the shredding process, a grading step can be performed to adjust the particle size of the powdered rubber to be used.

[0064] Crosslinked rubber can be recycled waste rubber, used rubber products, etc. Waste rubber is not limited to waste rubber generated from rubber products, but refers to all discarded rubber including unnecessary waste generated during the production or repair of rubber products. Examples of waste include buffing powder and peeling rubber. Buffing powder is, for example, fine rubber produced during the grinding process of retreading tires, where the tread portion remaining on the base tire is scraped off. Peeling rubber is, for example, long strips of rubber, 1-2 cm wide, peeled from the surface of rubber products (e.g., tires). Peeling rubber is generated by scraping the surface of rubber products such as tires using a knife with a U-shaped or V-shaped tip as a peeler. Rubber products include, for example, finished products such as tires, rubber hoses, rubber conveyor belts, and rubber parts or components in the manufacturing stage of the finished products. Waste tires can be retreaded tires, tires generated from tire replacement, vehicle scrapping, or ELTs (End-of-Life Tires) that have reached the end of their service life, or tires discarded for any reason.

[0065] -Diene-based rubber-

[0066] Diene-based rubber is a rubber containing units (diene units) derived from diene monomers, and may further contain units derived from copolymerizable comonomers.

[0067] Units derived from diene monomers enable crosslinking (vulcanization) of diene rubbers, imparting rubber-like tensile strength and properties. In crosslinked rubbers, diene rubbers typically exist in a crosslinked state, but a portion may be uncrosslinked. Specific examples of diene monomers (diene compounds) include 1,3-butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Among these, 1,3-butadiene and isoprene are preferred, with isoprene being particularly preferred.

[0068] On the other hand, examples of copolymerizable comonomers include aromatic vinyl compounds. Specific examples of such aromatic vinyl compounds include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o, p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene.

[0069] Examples of diene-based rubbers include isoprene-backed rubbers, styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). Here, isoprene-backed rubber is a rubber having isoprene units as its main backbone; specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). Preferably, the diene-based rubber comprises at least one selected from the group consisting of isoprene-backed rubber, styrene-butadiene rubber, and butadiene rubber, with isoprene-backed rubber being particularly preferred. When the diene-based rubber comprises at least one selected from the group consisting of isoprene-backed rubber, styrene-butadiene rubber, and butadiene rubber, a readily reusable liquid polymer containing diene monomers such as isoprene or butadiene as its backbone can be obtained by decomposing the crosslinked rubber and using recycled carbon black.

[0070] There is no particular limitation on the content of diene-based rubber in crosslinked rubber, but from the viewpoint of further improving the yield of liquid polymers containing diene-based monomers as a backbone, or butadiene or isoprene, it is preferred to be in the range of 10-100% by mass, and more preferably in the range of 30-100% by mass.

[0071] -Carbon Black-

[0072] There are no particular restrictions on carbon black. For example, carbon black grades include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762, etc.

[0073] There is no particular limitation on the carbon black content in the crosslinked rubber, and it is, for example, in the range of 10-150 parts by weight relative to 100 parts by weight of diene rubber, and preferably in the range of 30-120 parts by weight.

[0074] Furthermore, the carbon black content in the crosslinked rubber is preferably 20% by mass or more, more preferably 30% by mass or more, and more preferably 40% by mass or less, more preferably 35% by mass or less. When the carbon black content in the crosslinked rubber is 20% by mass or more, the amount of recyclable carbon black increases.

[0075] -Other components-

[0076] In addition to diene rubbers and carbon black, crosslinked rubbers can also contain various components commonly used in the rubber industry, such as rubber components other than diene rubbers, fillers other than carbon black (silica, calcium carbonate, etc.), silane coupling agents, antioxidants, softeners, processing aids, resins, surfactants, organic acids (such as stearic acid), zinc oxide (zinc white), vulcanization accelerators, and crosslinking agents (sulfur, peroxides, etc.).

[0077] (Methods for decomposing cross-linked rubber)

[0078] The recycled carbon black in this embodiment is obtained by decomposing crosslinked rubber, and can be obtained, for example, by the following:

[0079] (i) A method for decomposing cross-linked rubber using a metathesis catalyst (first decomposition method),

[0080] (ii) A method for thermally decomposing crosslinked rubber at temperatures above 150°C and below 400°C (second decomposition method).

[0081] (iii) A method for decomposing cross-linked rubber in a solvent (third decomposition method), or

[0082] (iv) A method for decomposing crosslinked rubber using a free radical initiator (fourth decomposition method).

[0083] Compared to the traditional high-temperature thermal decomposition of cross-linked rubber, the first, second, third, and fourth decomposition methods decompose at lower temperatures, resulting in more organic components, such as liquid polymers, remaining on the surface of the recycled carbon black. Furthermore, in these methods, the organic components of the recycled carbon black can be controlled by appropriately selecting the decomposition conditions. The first, second, third, and fourth decomposition methods will be described in detail below.

[0084] -First Decomposition Method (Complete Decomposition)-

[0085] In the first decomposition method, a metathesis catalyst is used to decompose the crosslinked rubber. Here, the metathesis catalyst is preferably a catalyst represented by the following general formula (1), (2) or (3):

[0086] [Chemical Formula 1]

[0087]

[0088] Catalysts of general formula (1), (2) or (3) are excellent at promoting metathesis and can easily (under mild conditions) and rapidly decompose diene rubbers.

[0089] In the above general formulas (1), (2) and (3), M is ruthenium (Ru), titanium (Ti), molybdenum (Mo) or tungsten (W). Among them, from the viewpoint of promoting the decomposition reaction of diene rubber in crosslinked rubber, ruthenium is preferred as M.

[0090] In the above general formulas (1) and (2), X 1 and X 2 Each ligand is represented independently, and anionic ligands are preferred. X 1 and X 2Examples include hydrogen, halogen, pseudohalogen, straight-chain or branched alkyl with 1 to 30 carbon atoms, aryl with 6 to 24 carbon atoms, alkoxy with 1 to 20 carbon atoms, aryloxy with 6 to 24 carbon atoms, alkyl diketoester with 3 to 20 carbon atoms, aryl diketoester with 6 to 24 carbon atoms, carboxylic acid ester with 1 to 20 carbon atoms, alkyl sulfonate with 1 to 20 carbon atoms, aryl sulfonate with 6 to 24 carbon atoms, alkyl thiol with 1 to 20 carbon atoms, aryl thiol with 6 to 24 carbon atoms, alkyl sulfonyl or alkyl sulfinyl with 1 to 20 carbon atoms.

[0091] The above X 1 and X 2 It may be substituted by one or more other groups such as halogen (preferably fluorine), alkyl with 1 to 10 carbon atoms, alkoxy with 1 to 10 carbon atoms, or aryl with 6 to 24 carbon atoms, and these groups themselves may be further substituted by one or more substituents selected from the group consisting of halogen (preferably fluorine), alkyl with 1 to 5 carbon atoms, alkoxy with 1 to 5 carbon atoms, and phenyl.

[0092] In the preferred embodiment, X 1 and X 2 They may be the same or different, and each may be a halogen (especially fluorine, chlorine, bromine or iodine), a benzoate, a carboxylic acid ester having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms, a phenoxy group, an alkoxy group having 1 to 5 carbon atoms, an alkyl thiol group having 1 to 5 carbon atoms, an aryl thiol group having 6 to 24 carbon atoms, an aryl group having 6 to 24 carbon atoms, or an alkyl sulfonate having 1 to 5 carbon atoms.

[0093] In a particularly preferred embodiment, X 1 and X 2 They are the same, and each is a halogen (especially chlorine), CF3COO, CH3COO, CFH2COO, (CH3)3CO, (CF3)2(CH3)CO, (CF3)(CH3)2CO, PhO (phenoxy), MeO (methoxy), EtO (ethoxy), toluene sulfonate (p-CH3-C6H4-SO3), mesitylene (2,4,6-trimethylphenyl) or CF3SO3 (trifluoromethanesulfonate).

[0094] In the above general formulas (1), (2) and (3), L 1 L 2 and L 3 Each ligand is represented independently, and is preferably a neutral (uncharged) electron donor (also known as an "electron-donating neutral ligand"). L 1 L 2 and L3 Each can be independently, for example, a phosphine, sulfonated phosphine, phosphate ester, phosphonate, phosphonite, arsine, antimony, ether, amine, amide, aryloxy, sulfonate, sulfoxide, carboxyl, nitrosyl, pyridine, thioether, or imidazolidine ligand. Preferably, L 1 L 2 and L 3 Each of the following is independently an arylphosphine ligand having 6 to 24 carbon atoms, an alkylphosphine ligand having 1 to 10 carbon atoms, or a cycloalkylphosphine ligand having 3 to 20 carbon atoms, a sulfonated arylphosphine ligand having 6 to 24 carbon atoms, or a sulfonated alkylphosphine ligand having 1 to 10 carbon atoms, an arylphosphite ligand having 6 to 24 carbon atoms, or an alkylphosphite ligand having 1 to 10 carbon atoms, an aryl phosphite ligand having 6 to 24 carbon atoms, or an alkyl phosphite ligand having 1 to 10 carbon atoms, or an aryl phosphite ligand having 6 to 24 carbon atoms, or an aryl phosphite ligand having 1 to 10 carbon atoms, or an aryl phosphite ligand having 6 to 24 carbon atoms. The ligand may be an alkylarsine or an alkylarsine ligand having 1 to 10 carbon atoms, an arylamine or an alkylamine ligand having 1 to 10 carbon atoms having 6 to 24 carbon atoms, a pyridine ligand, an aryl sulfoxide or an alkyl sulfoxide ligand having 1 to 10 carbon atoms having 6 to 24 carbon atoms, an aryl ether or an alkyl ether ligand having 1 to 10 carbon atoms having 6 to 24 carbon atoms, or an arylamide or an alkylamide ligand having 1 to 10 carbon atoms, and these may each be substituted with a phenyl group, and the phenyl group may optionally be further substituted with a halogen, an alkyl group having 1 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms.

[0095] The term "phosphine" includes, for example, PPh3, P(p-Tol)3, P(o-Tol)3, PPh(CH3)2, P(CF3)3, P(p-FC6H4)3, P(p-CF3C6H4)3, P(C6H4-SO3Na)3, P(CH2C6H4-SO3Na)3, P(isopropyl)3, P(CHCH3(CH2CH3))3, P(cyclopentyl)3, P(cyclohexyl)3, P(neopentyl)3, and P(neophenyl)3.

[0096] The term "phosphonates" includes, for example, triphenyl phosphonate, tricyclohexyl phosphonate, triisopropyl phosphonate, and methyl diphenyl phosphonate.

[0097] The term "phosphite" includes, for example, triphenyl phosphite, tricyclohexyl phosphite, tritert-butyl phosphite, triisopropyl phosphite, and methyl diphenyl phosphite.

[0098] The term "antimonide" includes, for example, triphenylantimony, tricyclohexylantimony, and trimethylantimony.

[0099] The term "aryloxy" includes, for example, 2-tert-butyl-4,5-dimethylphenoxy.

[0100] The term "sulfonate" includes, for example, trifluoromethanesulfonates, toluenesulfonates, and methanesulfonates.

[0101] The term "sulfone" includes, for example, (CH3)2S(=O) and (C6H5)2S=O.

[0102] The term "thioether" includes, for example, CH3SCH3, C6H5SCH3, CH3OCH2CH2SCH3 and tetrahydrothiophene.

[0103] The term "pyridine" includes, for example, pyridine, picolin (α-, β- and γ-picolin), rutidine (2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-rutidine), chloridine (2,4,6-trimethylpyridine), trifluoromethylpyridine, phenylpyridine, 4-(dimethylamino)pyridine, chloropyridine, bromopyridine, nitropyridine, quinoline, pyrimidine, pyrrole, imidazole and phenylimidazolium.

[0104] In imidazolidine ligands, the hydrogen atoms bonded to the carbon or nitrogen atoms constituting the imidazolidine ring may be substituted with straight-chain or branched alkyl groups having 1 to 30 carbon atoms, cycloalkyl groups having 3 to 20 carbon atoms, alkenyl groups having 2 to 20 carbon atoms, alkynyl groups having 2 to 20 carbon atoms, aryl groups having 6 to 24 carbon atoms, carboxylic acid esters having 1 to 20 carbon atoms, alkoxy groups having 1 to 20 carbon atoms, alkenyloxy groups having 2 to 20 carbon atoms, alkynyloxy groups having 2 to 20 carbon atoms, aryloxy groups having 6 to 20 carbon atoms, alkoxycarbonyl groups having 2 to 20 carbon atoms, alkylthio groups having 1 to 20 carbon atoms, arylthio groups having 6 to 20 carbon atoms, alkylsulfonyl groups having 1 to 20 carbon atoms, alkylsulfonates having 1 to 20 carbon atoms, arylsulfonates having 6 to 20 carbon atoms, or alkylsulfinyl groups having 1 to 20 carbon atoms.

[0105] In the above general formulas (1), (2) and (3), R 1 R 2 and R 3 Each of these groups independently represents hydrogen, alkyl, cycloalkyl, alkenyl, alkynyl, aryl, aralkyl, carboxylate, alkoxy, alkenyloxy, alkynyloxy, alkoxycarbonyl, alkylamino, alkylthio, arylthio, alkylsulfonyl, or alkylsulfinyl, wherein these groups may be substituted by one or more alkyl, halogen, alkoxy, aryl, or heteroaryl groups.

[0106] Furthermore, as an alkyl group, an alkyl group having 1 to 30 carbon atoms is preferred; as a cycloalkyl group, a cycloalkyl group having 3 to 20 carbon atoms is preferred; as an alkenyl group, an alkenyl group having 2 to 20 carbon atoms is preferred; as an alkynyl group, an alkynyl group having 2 to 20 carbon atoms is preferred; as an aryl group, an aryl group having 6 to 24 carbon atoms is preferred; as an aralkyl group, an aralkyl group having 7 to 24 carbon atoms is preferred; as a carboxylate group, a carboxylate group having 1 to 20 carbon atoms is preferred; as an alkoxy group, an alkoxy group having 1 to 20 carbon atoms is preferred; as an alkenoxy group, an alkenoxy group having 2 to 20 carbon atoms is preferred. As an alkynyloxy group, an alkynyloxy group with 2 to 20 carbon atoms is preferred; as an aryloxy group, an aryloxy group with 6 to 24 carbon atoms is preferred; as an alkoxycarbonyl group, an alkoxycarbonyl group with 2 to 20 carbon atoms is preferred; as an alkylamino group, an alkylamino group with 1 to 30 carbon atoms is preferred; as an alkylthio group, an alkylthio group with 1 to 30 carbon atoms is preferred; as an arylthio group, an arylthio group with 6 to 24 carbon atoms is preferred; as an alkylsulfonyl group, an alkylsulfonyl group with 1 to 20 carbon atoms is preferred; and as an alkylsulfinyl group, an alkylsulfinyl group with 1 to 20 carbon atoms is preferred.

[0107] In one implementation, R 1 and R 2 One of them is hydrogen, and the other is an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aryl group having 6 to 24 carbon atoms, an aralkyl group having 7 to 24 carbon atoms, a carboxylate group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an alkenyloxy group having 2 to 20 carbon atoms, an alkynyloxy group having 2 to 20 carbon atoms, an aryloxy group having 6 to 24 carbon atoms, an alkoxycarbonyl group having 2 to 20 carbon atoms, an alkylamino group having 1 to 30 carbon atoms, an alkylthio group having 1 to 30 carbon atoms, an arylthio group having 6 to 24 carbon atoms, an alkylsulfonyl group having 1 to 20 carbon atoms, or an alkylsulfinyl group having 1 to 20 carbon atoms, and each of these groups may be substituted by one or more alkyl, halogen, alkoxy, aryl, or heteroaryl groups.

[0108] In the above general formulas (1), (2) and (3), L 1 and L 2 They can bond together to form a ring. Through L... 1 and L 2 The bonded ring can be aliphatic or aromatic and can optionally be substituted and contain one or more heteroatoms. Examples of heteroatoms include oxygen, sulfur, nitrogen, and phosphorus.

[0109] In the above general formulas (1), (2) and (3), R 1 and R 2They can bond together to form a ring. (Through R...) 1 and R 2 The rings formed together with the common carbon atoms bonded to them can be aliphatic or aromatic, and can optionally be substituted and contain one or more heteroatoms.

[0110] In the above general formulas (1), (2) and (3), L 1 and R 1 They can bond together to form a ring. Through L... 1 and R 1 The bonded ring can be aliphatic or aromatic and can optionally be substituted and contain one or more heteroatoms. Examples of heteroatoms include oxygen, sulfur, nitrogen, and phosphorus.

[0111] As a catalyst represented by the above general formula (1), a catalyst represented by the following structural formulas (1-1) to (1-3) is preferred:

[0112] [Chemical Formula 2]

[0113]

[0114] [In the formula, Cy represents cyclohexyl, and Mes represents mesityleneyl (also known as "2,4,6-trimethylphenyl")].

[0115] Catalysts with structural formula (1-1) are called Grubbs first-generation catalysts, catalysts with structural formula (1-2) are called Grubbs second-generation catalysts, and catalysts with structural formula (1-3) are called Grubbs-Hoveyda second-generation catalysts. When using catalysts represented by any of structural formulas (1-1) to (1-3), the decomposition reaction (metathesis) of diene rubber in crosslinked rubber proceeds more rapidly.

[0116] As a catalyst represented by the above general formula (2), a catalyst represented by the following structural formula (2-1) is preferred:

[0117] [Chemical Formula 3]

[0118] .

[0119] The catalyst with structural formula (2-1) is called the Grubbs third-generation catalyst. When using a catalyst represented by structural formula (2-1), the decomposition reaction (metathesis) of diene rubber in crosslinked rubber proceeds more rapidly.

[0120] As a catalyst represented by the above general formula (3), a catalyst represented by the following structural formula (3-1) may be mentioned:

[0121] [Chemical Formula 4]

[0122] .

[0123] The amount of catalyst relative to 100 parts by mass of diene rubber is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and more preferably 10 parts by mass or less, more preferably 8 parts by mass or less. If the amount of catalyst is 0.1 parts by mass or more relative to 100 parts by mass of diene rubber, the decomposition reaction of diene rubber proceeds further, and if the amount of catalyst is 10 parts by mass or less relative to 100 parts by mass of diene rubber, it is preferred from a cost point of view.

[0124] The decomposition by the metathesis catalyst (hereinafter sometimes simply referred to as "metathesis") is preferably carried out at a temperature of 20°C or higher and 200°C or lower. By carrying out metathesis at a temperature of 20°C or higher, the decomposition rate of the diene rubber in the crosslinked rubber is improved, and by carrying out metathesis at a temperature of 200°C or lower, the decomposition of the catalyst (metathesis catalyst) represented by the above general formulas (1), (2), or (3) can be suppressed, and after decomposition, the retention rate (selectivity) of the monomer backbone of the diene rubber in the crosslinked rubber is improved. From the viewpoint of improving the decomposition rate of the diene rubber, metathesis is more preferably carried out at a temperature of 25°C or higher, and from the viewpoint of suppressing the decomposition of the metathesis catalyst and improving the selectivity of the product that retains the monomer backbone, it is more preferably carried out at a temperature of 100°C or lower.

[0125] Metathesis can be carried out under any pressure, including reduced pressure, atmospheric pressure, or high pressure. As an example, the reaction pressure is preferably from 1 kPa to 10 MPa, more preferably from 10 kPa to 1 MPa, and even more preferably from 50 kPa to 500 kPa.

[0126] In metathesis, the catalyst represented by the above general formulas (1), (2), or (3) can be dissolved in the solvent, or the crosslinked rubber can be immersed in the solvent. By allowing the catalyst to act on the crosslinked rubber in the solvent, the decomposition reaction of the diene rubber in the crosslinked rubber is more easily carried out.

[0127] Here, any solvent that does not inhibit the decomposition reaction can be used as a solvent, and examples include ethers, aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons (aromatic solvents). More specifically, tetrahydrofuran (THF), hexane, cyclohexane, pentane, cyclopentane, toluene, and xylene are preferred solvents, with toluene and tetrahydrofuran being more preferred. When the solvent is selected from tetrahydrofuran, hexane, cyclohexane, pentane, cyclopentane, toluene, and xylene, the decomposition reaction of the diene rubber in the crosslinked rubber is even more readily carried out.

[0128] The amount of solvent relative to 1g of crosslinked rubber is preferably 10mL or more, more preferably 50mL or more, and more preferably 500mL or less, more preferably 200mL or less. If the amount of solvent is 10mL or more relative to 1g of crosslinked rubber, the decomposition reaction of the diene rubber in the crosslinked rubber proceeds further, and if the amount of solvent is 500mL or less relative to 1g of crosslinked rubber, it is preferred from a cost point of view.

[0129] Metathesis can occur in the presence of a chain transfer agent (CTA). Examples of chain transfer agents include cis-1,4-diacetoxy-2-butene and cis-1,4-dibenzyloxy-2-butene.

[0130] The amount of chain transfer agent is preferably in the range of 1-100 mol relative to 1 mol of catalyst.

[0131] The recycled carbon black obtained through the above metathesis contains components derived from the metathesis catalyst, such as ruthenium (Ru), titanium (Ti), molybdenum (Mo), tungsten (W), and phosphorus (P), and the components derived from the metathesis catalyst, such as Ru, Ti, Mo, W, and P, can be used as markers. For example, by reusing the recycled carbon black obtained through metathesis in a rubber composition and measuring the content of Ru, Ti, Mo, W, and P in the rubber composition, the content of recycled carbon black in the rubber composition can be calculated.

[0132] -Second decomposition method (low-temperature pyrolysis)-

[0133] In the second decomposition method, the crosslinked rubber is thermally decomposed at a temperature above 150°C and below 400°C. By conducting the thermal decomposition at a temperature above 150°C, the decomposition reaction rate of the diene rubber in the crosslinked rubber is improved, and by conducting the thermal decomposition at a temperature below 400°C, the vaporization and aromatization of the decomposition products can be suppressed. Furthermore, after decomposition, the retention rate (selectivity) of the monomer backbone of the diene rubber in the crosslinked rubber is improved. From the viewpoint of improving the decomposition reaction rate of the diene rubber, the thermal decomposition is preferably carried out at a temperature above 175°C, more preferably above 190°C. In addition, from the viewpoint of improving the selectivity of products that retain the monomer backbone, it is preferably carried out at a temperature below 350°C, more preferably below 300°C.

[0134] The second decomposition method is preferably carried out under a non-reactive gas atmosphere. By conducting thermal decomposition under a non-reactive gas atmosphere, the oxidation and reduction of the decomposition products can be suppressed, and in particular, the hydrogenation of double bonds in oligomers or monomers in the decomposition products can be suppressed. Furthermore, the oxidation of recycled carbon black can also be suppressed. Examples of non-reactive gases include nitrogen, carbon dioxide, argon, and helium.

[0135] To perform the above pyrolysis in a non-reactive gas atmosphere, for example, when using a batch reactor, it is sufficient to set the atmosphere in the reactor to a non-reactive gas, and when using a flow-through reactor, it is sufficient to set the atmosphere flowing through the reactor to a non-reactive gas. Note that although hydrogen may be generated during pyrolysis, the generated hydrogen is not considered in the pyrolysis atmosphere.

[0136] The pyrolysis described above can be carried out under any pressure, including under reduced pressure, atmospheric pressure, or pressurized pressure, but is preferably carried out under reduced pressure or atmospheric pressure. As an example, the reaction pressure for pyrolysis is preferably between 1000 kPa and 65 kPa. By carrying out pyrolysis under reduced pressure or atmospheric pressure, the polymerization (repolymerization) of oligomers and monomers in the decomposition products can be suppressed.

[0137] There is no particular limitation on the reaction time of the above pyrolysis. As an example, the reaction time of pyrolysis is preferably from 1 minute to 180 minutes, more preferably from 3 minutes to 60 minutes, and even more preferably from 5 minutes to 30 minutes.

[0138] The pyrolysis described above can be carried out with or without a catalyst, but it is preferred to do so without a catalyst. Costs can be reduced by not using a catalyst in the pyrolysis. Note that when a catalyst is used, any catalyst that promotes the decomposition reaction of the crosslinked rubber can be used.

[0139] -Third decomposition method (solvation)-

[0140] In the third decomposition method, the cross-linked rubber is decomposed in a solvent. When the decomposition of the cross-linked rubber takes place in a solvent, the cross-linked rubber swells due to the solvent. By decomposing the cross-linked rubber under solvent swelling, the vaporization and aromatization of the decomposition products can be suppressed, and compared with conventional high-temperature pyrolysis, decomposition products (liquid polymers) with a higher retention rate of the backbone structure of the constituent monomers of diene rubbers (isoprene backbone, butadiene backbone, etc.) can be obtained.

[0141] As the solvents described above, various solvents that cause crosslinked rubber to swell can be used, such as aromatic solvents, aliphatic solvents, alicyclic solvents, and ester solvents. Examples of aromatic solvents include benzene, toluene, and xylene; examples of aliphatic solvents include pentane, hexane, and heptane; examples of alicyclic solvents include cyclopentane and cyclohexane; and examples of ester solvents include ethyl acetate, propyl acetate, and butyl acetate. Among these, at least one solvent selected from the group consisting of toluene, xylene, and cyclohexane is preferred, with toluene being particularly preferred. By using toluene, xylene, or cyclohexane as a solvent, decomposition products (liquid polymers) with a high retention rate of the backbone structure (isoprene backbone, butadiene backbone, etc.) of the constituent monomers of diene rubber can be obtained.

[0142] The amount of solvent used is preferably 1 mL or more, more preferably 5 mL or more, and more preferably 500 mL or less, more preferably 200 mL or less, relative to 1 g of crosslinked rubber. If the amount of solvent is 10 mL or more relative to 1 g of crosslinked rubber, the decomposition reaction of the diene rubber in the crosslinked rubber will proceed further, and if the amount of solvent is 500 mL or less relative to 1 g of crosslinked rubber, it is preferred from a cost point of view.

[0143] The decomposition temperature in the aforementioned solvent is preferably between 150°C and 300°C. By decomposing in the solvent at temperatures above 150°C, the decomposition rate of the diene rubber in the crosslinked rubber is improved. Furthermore, by decomposing in the solvent at temperatures below 300°C, high-quality carbon black can be recovered and reused, the vaporization and aromatization of decomposition products are suppressed, and the retention rate (selectivity) of the monomer backbone structure of the diene rubber in the crosslinked rubber is improved after decomposition. From the viewpoint of improving the decomposition rate of the crosslinked rubber in the aforementioned solvent, temperatures above 180°C are preferred, and even more preferably above 200°C. From the viewpoint of improving the selectivity of products that retain the monomer backbone, temperatures below 260°C are preferred, and more preferably below 240°C.

[0144] There is no particular limitation on the decomposition time in the aforementioned solvent. As an example, the decomposition time in the aforementioned solvent is preferably 1 hour to 48 hours, more preferably 3 hours to 18 hours. By carrying out decomposition in the aforementioned solvent for more than 3 hours, the decomposition rate of the crosslinked rubber is improved. On the other hand, if the reaction time becomes too long, the backbone (double bonds, etc.) of the constituent monomers of the diene rubber may decompose, or the decomposition products may vaporize or aromatize. However, by carrying out decomposition in the solvent for less than 18 hours, the decomposition of the monomer backbone and the vaporization or aromatization of the decomposition products can be suppressed, and after decomposition, the retention rate (selectivity) of the backbone structure of the constituent monomers of the diene rubber in the crosslinked rubber is improved.

[0145] The decomposition is preferably carried out in the solvent under a non-reactive gas atmosphere. By decomposing in the solvent under a non-reactive gas atmosphere, the amount of active substances (oxygen, hydrogen, etc.) dissolved in the solvent can be reduced, thereby inhibiting the oxidation or reduction of the decomposition products, especially the oxidation of recycled carbon black, and the hydrogenation of double bonds in oligomers or monomers in the decomposition products. Examples of non-reactive gases include nitrogen, carbon dioxide, argon, and helium.

[0146] To carry out decomposition in the aforementioned solvent under a non-reactive gas atmosphere, for example, when using a batch reactor, it is sufficient to set the atmosphere in the reactor to a non-reactive gas, and when using a flow-through reactor, it is sufficient to set the atmosphere flowing through the reactor to a non-reactive gas. Note that although hydrogen may be generated during decomposition in the solvent, the generated hydrogen is not considered in the atmosphere of decomposition in the solvent.

[0147] The decomposition in the solvent described above can be carried out under any pressure, including under reduced pressure, at atmospheric pressure, or under pressure. As an example, the reaction pressure is preferably from 1 kPa to 10 MPa, more preferably from 10 kPa to 5 MPa, and even more preferably from 50 kPa to 2 MPa.

[0148] The decomposition in the aforementioned solvent can be carried out with or without a catalyst, but it is preferred to do so without a catalyst. Costs can be reduced by not using a catalyst in the decomposition in the solvent. Note that when a catalyst is used, any catalyst that promotes the decomposition reaction of the crosslinked rubber can be used.

[0149] -Fourth Decomposition Method (Free Radical Decomposition)-

[0150] In the fourth decomposition method, a free radical initiator is applied to the crosslinked rubber under an oxygen-containing atmosphere. It is believed that the free radical initiator primarily acts on the crosslinking sites formed by sulfur, thereby breaking the crosslinking bonds. Therefore, in the case of diene-based rubbers, it is assumed that the main chain backbone is essentially maintained even after the decomposition reaction.

[0151] Various conventionally known types can be used as free radical initiators, but from the viewpoint of reaction efficiency, peroxides and azo compounds are preferred, with peroxides being more preferred.

[0152] Examples of peroxides include acyl peroxides, percarboxylic acids, dialkyl peroxides, and alkyl hydroperoxides. From the viewpoint of reaction rate, acyl peroxides and percarboxylic acids are preferred, and acyl peroxides are more preferred.

[0153] Specific examples include benzoyl peroxide, methyl benzoyl peroxide, chlorobenzoyl peroxide, dichlorobenzoyl peroxide, methoxybenzoyl peroxide, phthaloyl peroxide, acetyl peroxide, propionyl peroxide, octanoyl peroxide, decanyl peroxide, lauroyl peroxide, myristoyl peroxide, and stearyl peroxide, among other acyl peroxides. From the viewpoints of reaction rate, cost, and ease of procurement, benzoyl peroxide, lauroyl peroxide, and acetyl peroxide are preferred among acyl peroxides. From the viewpoints of reaction rate and peroxide stability, lauroyl peroxide is superior to benzoyl peroxide.

[0154] In addition, percarboxylic acids such as perbenzoic acid, chloroperbenzoic acid, peracetic acid, and perpropionic acid can be mentioned. Furthermore, as dialkyl peroxides, di-tert-butyl peroxide, dicumyl peroxide, and tert-butyl cumyl peroxide can be mentioned, and as alkyl hydroperoxides, tert-butyl hydroperoxide and cumyl hydroperoxide can be mentioned.

[0155] On the other hand, as azo compounds, azobisisobutyronitrile, azobis-2,4-dimethylpentanonitrile, azobiscyclohexaneformitrile, and methyl azobisisobutyrate can be mentioned.

[0156] From a safety and ease of procurement perspective, these free radical initiators can be in hydrate form. By using suitable initiators, crosslinked rubbers can be efficiently decomposed under mild conditions.

[0157] The amount of the free radical initiator used is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and more preferably 30 parts by mass or less, more preferably 20 parts by mass or less, relative to 100 parts by mass of crosslinked rubber. If the amount of the free radical initiator is 0.1 parts by mass or more relative to 100 parts by mass of crosslinked rubber, the decomposition reaction of the crosslinked rubber proceeds more rapidly, and if the amount of the free radical initiator is 30 parts by mass or less relative to 100 parts by mass of crosslinked rubber, it is preferred from a cost point of view.

[0158] The aforementioned fourth decomposition method is carried out in an atmosphere containing oxygen. The concentration (volume %) of oxygen in the reaction atmosphere is typically 1 to 100%, preferably 1 to 80%, and more preferably 5 to 50% (including approximately 20% oxygen concentration in the air). If the oxygen concentration is not 100%, an inert gas such as nitrogen can be used as the residual gas component. Generally, the higher the oxygen concentration, the more favorable the decomposition reaction of the fourth decomposition method, but the more likely undesirable side reactions may occur. Therefore, when the oxygen concentration is high, it is preferable to appropriately control the reaction time and reaction temperature, etc.

[0159] On the other hand, when using atmospheric air with an oxygen concentration of approximately 20%, there is no need to prepare oxygen separately, which is advantageous in terms of equipment and economy. In reactions under an air atmosphere, if the amount of crosslinked rubber is small, the reaction can even take place in a closed system container with a sufficiently large internal volume. In this case, the internal volume of the reaction container is typically 50 parts by volume or more, more preferably 100 parts by volume or more, relative to 1 part by volume of crosslinked rubber.

[0160] When the fourth decomposition method is carried out in a closed system, if the amount of crosslinked rubber increases, a reaction vessel with a large internal volume is required, which is not preferred from an equipment viewpoint. Therefore, from an equipment viewpoint, it is preferable to carry out the reaction in a non-closed system where air or the like can circulate. To prevent the reaction system from being closed, methods such as opening a portion of the reaction vessel, installing a membrane that allows air or the like to circulate, or allowing air or the like to overflow can be considered. Furthermore, methods of continuously or intermittently blowing air or the like into the solution during the reaction are also advantageous. In this case, there is no particular limitation on the blowing rate, but it is typically 1 to 1000 mL / min relative to 1 g of crosslinked rubber, preferably 2 to 500 mL / min, and more preferably 3 to 200 mL / min.

[0161] In the fourth decomposition method described above, the free radical initiator can be dissolved in a solvent for use, or the crosslinked rubber can be immersed in a solvent for decomposition. Applying the free radical initiator to the crosslinked rubber in a solvent promotes its decomposition.

[0162] Here, any solvent that does not inhibit the decomposition reaction can be used as the solvent mentioned above, and examples include aromatic hydrocarbons (aromatic solvents), chlorinated hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, and ethers.

[0163] Specifically, examples include toluene, xylene, ethylbenzene, trimethylbenzene, and propylbenzene as aromatic hydrocarbons; chloroform, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, tetrachloroethylene, chlorobenzene, and dichlorobenzene as chlorinated hydrocarbons; pentane, hexane, and octane as aliphatic hydrocarbons; cyclopentane, cyclohexane, and cyclooctane as alicyclic hydrocarbons; and tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, and dioxane as ethers.

[0164] From the perspective of reaction rate and ease of procurement, aromatic hydrocarbons and chlorinated hydrocarbons are preferred. Specific examples include toluene, xylene, ethylbenzene, chloroform, chlorobenzene, and dichlorobenzene. Among aromatic hydrocarbons, ethylbenzene is superior to toluene from the viewpoint of reaction rate.

[0165] The solvent suitable for the decomposition reaction also depends on the type of crosslinked rubber. For example, in the case of NR, IR, or BR type crosslinked rubbers, aromatic hydrocarbons and chlorinated hydrocarbons are preferred from the viewpoint of reaction rate and product solubility, and specific examples include toluene, ethylbenzene, chloroform, and chlorobenzene. On the other hand, in the case of SBR type crosslinked rubbers, chlorinated hydrocarbons are more preferred from the viewpoint of reaction rate, and specific examples include chloroform and chlorobenzene.

[0166] By using a preferred solvent, the decomposition of cross-linked rubber is promoted, and liquid polymers can be produced more efficiently.

[0167] The amount of solvent used is preferably 2 mL or more, more preferably 10 mL or more, and more preferably 100 mL or less, and more preferably 50 mL or less, relative to 1 g of crosslinked rubber. If the amount of solvent is 2 mL relative to 1 g of crosslinked rubber, it promotes the decomposition reaction of the crosslinked rubber, and if the amount of solvent is 50 mL or less relative to 1 g of crosslinked rubber, it is preferred from a cost point of view.

[0168] The aforementioned fourth decomposition method is preferably carried out at a temperature above 0°C and below 200°C. By carrying out the fourth decomposition method at a temperature above 0°C, the decomposition reaction rate of the crosslinked rubber is improved, and by carrying out the fourth decomposition method at a temperature below 200°C, the retention rate (selectivity) of the monomer backbone in the crosslinked rubber is improved.

[0169] From the viewpoint of improving the decomposition reaction rate of crosslinked rubber, the above-mentioned fourth decomposition method is more preferably above 10°C, and from the viewpoint of improving the selectivity of products that maintain the monomer skeleton, it is more preferably below 150°C.

[0170] Furthermore, when using peroxide-type free radical initiators, the decomposition efficiency is high, thus the reaction proceeds at low temperatures below 60°C. Even near room temperature (20°C to 30°C), the reaction proceeds smoothly, therefore no special heating or cooling equipment is required, which is also an advantage when using peroxide-type free radical initiators.

[0171] The fourth decomposition method described above can be carried out under any pressure, including under reduced pressure, atmospheric pressure, or under increased pressure. Specifically, the reaction pressure is preferably from 1 kPa to 10 MPa, more preferably from 10 kPa to 1 MPa, and even more preferably from 50 kPa to 500 kPa.

[0172] In the fourth decomposition method described above, it is crucial to effectively stir the raw materials, including the crosslinked rubber, the free radical initiator, and the solvent. Various conventionally known methods can be used for stirring, such as magnetic stirrers, mechanical stirrers, or vibrators.

[0173] In addition, ultrasonic irradiation, microwave irradiation, and light irradiation can be used to promote the reaction. These can also be used in combination.

[0174] -Other decomposition methods-

[0175] The method for decomposing crosslinked rubber to obtain the recycled carbon black of this embodiment is not limited to the first, second, third, and fourth decomposition methods described above, and any decomposition method can be used as long as the basic structure of the polymer is maintained at 30% or more. Furthermore, a decomposition method in which the polymer structure is maintained at 50% or more is preferred, and even more preferred is a decomposition method in which the polymer structure is maintained at 70% or more.

[0176] -Separation-

[0177] According to the first, second, third, and fourth decomposition methods described above, the crosslinked rubber can be decomposed and reduced to a low molecular weight until it becomes a liquid polymer. Therefore, after the decomposition reaction, carbon black can be easily separated and collected from the decomposition products, for example, by centrifugation or filtration. Note that the recycled carbon black of this embodiment is preferably obtained by centrifugation from the decomposition products after the crosslinked rubber has decomposed. By centrifuging, recycled carbon black containing more than 5% by mass of organic components can be easily obtained. Here, as conditions for centrifugation, for example, a centrifugal acceleration in the range of 200 to 200,000 G is preferred, and a rotation time in the range of 60 seconds to 180 minutes is preferred.

[0178] -washing-

[0179] A washing step is preferably performed on the recycled carbon black obtained by separation and collection as described above. By performing the washing step, recycled carbon black with a small amount of impurities can be easily obtained. Washing is preferably performed using, for example, an organic solvent. The recycled carbon black of this embodiment contains more than 5% by mass of the organic components remaining in the recycled carbon black after washing with toluene, therefore it has excellent dispersibility in organic solvents, and impurities can be easily reduced by washing with an organic solvent. Here, aromatic solvents such as toluene and xylene, aliphatic solvents such as hexane, and alicyclic solvents such as cyclohexane can be used as organic solvents.

[0180] -dry-

[0181] The recycled carbon black that has undergone the washing steps described above is preferably dried at room temperature, heated, or under vacuum to remove organic solvents and moisture. When heated or under vacuum is performed, the heating temperature is preferably below 200°C, more preferably below 150°C, and even more preferably below 100°C.

[0182] (use)

[0183] The recycled carbon black of this embodiment can be used as a filler in rubber compositions for various rubber products.

[0184] Besides rubber compositions, the recycled carbon black of this embodiment can also be used in black inks, etc. Here, when used in black inks, recycled carbon black with a fine particle size is preferred.

[0185]

[0186] The mixture of recycled carbon black and liquid polymer according to the first embodiment of this disclosure is a mixture of recycled carbon black and liquid polymer obtained by decomposing a crosslinked rubber comprising diene rubber and carbon black. In the mixture of recycled carbon black and liquid polymer of the first embodiment, the recycled carbon black is the recycled carbon black of the present embodiment described above (in other words, the recycled carbon black after toluene washing has a residual organic component of more than 5% by mass), and the liquid polymer is characterized in that its weight average molecular weight is less than 300,000.

[0187] Herein, in this specification, the term "liquid polymer" refers to a substance that is liquid at room temperature (23°C) and contains two or more diene monomer units.

[0188] The mixture of recycled carbon black and liquid polymer in the first embodiment can be obtained after the aforementioned crosslinked rubber decomposition without separating or collecting the recycled carbon black. By incorporating the mixture of recycled carbon black and liquid polymer into the rubber composition without separating or collecting the recycled carbon black, the productivity of the rubber composition can be improved.

[0189] Furthermore, when the mixture of recycled carbon black and liquid polymer of this first embodiment is reused in the rubber composition, the liquid polymer acts as a softener, making the rubber composition easier to knead.

[0190] In the mixture of recycled carbon black and liquid polymer in the first embodiment, the weight-average molecular weight of the liquid polymer is preferably from 500 to 250,000, and in any case, from 300,000 to below. The weight-average molecular weight of the liquid polymer can vary depending on the decomposition method and conditions of the crosslinked rubber. For example, a liquid polymer with a weight-average molecular weight of 500 to 30,000 can be readily obtained according to the third decomposition method (solvent hydrolysis).

[0191] Note that in this specification, the weight-average molecular weight (Mw) is measured by gel permeation chromatography (GPC).

[0192] The mixture of recycled carbon black and liquid polymer according to the second embodiment of this disclosure is a mixture of recycled carbon black and liquid polymer obtained by decomposing a crosslinked rubber comprising diene rubber and carbon black. In the mixture of recycled carbon black and liquid polymer of the second embodiment, the recycled carbon black is the recycled carbon black of the present embodiment described above (in other words, the recycled carbon black after toluene washing has a residual organic component of 5% by mass or more), and the liquid polymer is characterized in that the proportion of the component with a molecular weight of 15,000 or less is 30% by mass or less.

[0193] The mixture of recycled carbon black and liquid polymer in the second embodiment can be obtained after the decomposition of the aforementioned crosslinked rubber by removing some or all of the low molecular weight components from the liquid polymer without separating or collecting the recycled carbon black. By incorporating the mixture of recycled carbon black and liquid polymer into the rubber composition without separating or collecting the recycled carbon black, the productivity of the rubber composition can be improved. Furthermore, by removing some or all of the low molecular weight components from the liquid polymer, the plasticizing effect caused by the low molecular weight components can be suppressed when the mixture of recycled carbon black and liquid polymer is incorporated into the rubber composition, making it easier to obtain a rubber composition with the desired physical properties.

[0194] In the mixture of recycled carbon black and liquid polymer in the second embodiment, the proportion of the component of liquid polymer with a molecular weight of 15,000 or less is 30% by mass or less. When the proportion of the component with a molecular weight of 15,000 or less is 30% by mass or less, the plasticizing effect can be suppressed, making it easier to obtain a rubber composition with the desired physical properties.

[0195] Here, gel permeation chromatography (GPC) is used to measure molecular weight.

[0196] <Rubber Composition>

[0197] The rubber composition according to the first embodiment of the present invention is characterized in that it comprises a rubber component and the aforementioned recycled carbon black. Since the rubber composition of the first embodiment comprises the recycled carbon black of this embodiment, environmental impact can be reduced while maintaining physical properties. Here, the amount of recycled carbon black is preferably in the range of 10 to 100 parts by weight relative to 100 parts by weight of the rubber component.

[0198] Furthermore, the rubber composition according to the second embodiment of this disclosure is characterized in that it comprises a rubber component and a mixture of recycled carbon black and a liquid polymer according to the first embodiment of this disclosure. Since the rubber composition of the second embodiment comprises the aforementioned mixture of recycled carbon black and liquid polymer, environmental impact can be reduced while maintaining physical properties. Here, the amount of the mixture of recycled carbon black and liquid polymer is preferably in the range of 10 to 100 parts by weight relative to 100 parts by weight of the rubber component.

[0199] Furthermore, the rubber composition according to the third embodiment of this disclosure is characterized in that it comprises a rubber component and a mixture of recycled carbon black and a liquid polymer according to the second embodiment of this disclosure (i.e., a mixture from which some or all of the low molecular weight components of the liquid polymer have been removed). Since the rubber composition of the third embodiment comprises the aforementioned mixture of recycled carbon black and liquid polymer, environmental impact can be reduced while maintaining physical properties. Here, the amount of the mixture of recycled carbon black and liquid polymer is preferably in the range of 10 to 100 parts by weight relative to 100 parts by weight of the rubber component.

[0200] The rubber compositions of the first, second and third embodiments described above are all suitable as rubber compositions for tires because their physical properties, such as tensile strength (TB) and elongation at break (EB), are maintained.

[0201] Each rubber composition comprises a rubber component that imparts rubber elasticity to the composition. Diene-based rubbers are preferred as rubber components, and examples of diene-based rubbers include isoprene-backed rubbers, styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). Here, isoprene-backed rubber refers to rubber having isoprene units as the main backbone; specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). These rubber components can be used alone or as blends of two or more types.

[0202] In addition to the aforementioned rubber components, recycled carbon black, and mixtures of recycled carbon black and liquid polymers, rubber compositions may also contain compounding agents commonly used in the rubber industry, such as fillers (carbon black, silica, calcium carbonate, etc.), silane coupling agents, antioxidants, waxes, softeners, processing aids, resins, surfactants, organic acids (e.g., stearic acid), zinc oxide (zinc white), vulcanization accelerators, and crosslinking agents (sulfur, peroxides, etc.).

[0203] In the rubber composition, the recycled carbon black of this embodiment can be used in combination with unused carbon black or other recycled carbon black (i.e., carbon black in which the residual organic component after toluene washing is less than 5% by mass). Here, the proportion of the recycled carbon black of this embodiment in the total carbon black is preferably 10% by mass or more, and can be up to 100% by mass. The carbon black used in combination with the recycled carbon black of this embodiment preferably has a dibutyl phthalate (DBP) absorption of 40-200 mL / 100 g. Furthermore, the carbon black used in combination with the recycled carbon black of this embodiment preferably has a absorption of 20-180 mL / 100 g. 2 / g of nitrogen adsorption specific surface area (N2SA).

[0204] Note that in this specification, the dibutyl phthalate (DBP) absorption of carbon black is determined according to JIS K 6217-4:2017. Furthermore, in this specification, the nitrogen adsorption specific surface area (N2SA) of carbon black is determined according to JIS K 6217-2:2017.

[0205] In the rubber composition, the recycled carbon black of this embodiment can be used in combination with silica. The silica used in combination with the recycled carbon black of this embodiment preferably has an average particle size of 0.1 to 100 μm.

[0206] Note that in this specification, the average particle size of silica is the average particle size measured by light scattering using a particle size distribution measuring device.

[0207] Furthermore, when the recycled carbon black of this embodiment is incorporated into the rubber composition, the rubber component of the rubber composition may be the same as or different from the diene rubber contained in the crosslinked rubber (i.e., the raw material of the recycled carbon black of this embodiment).

[0208] The recycled carbon black of this embodiment can be incorporated into the rubber composition as a wet masterbatch. When incorporated as a wet masterbatch, the recycled carbon black of this embodiment can be dispersed in any solvent (organic solvent, water, etc.) and incorporated into the rubber composition, or it can be incorporated into the rubber composition as a mixture with the above-mentioned liquid polymer.

[0209] Rubber Products

[0210] The rubber article of this embodiment is characterized in that it comprises a rubber component made of the rubber composition of the first, second, or third embodiment described above. Because the rubber article of this embodiment comprises a rubber component formed from the aforementioned rubber composition, it retains its physical properties.

[0211] Examples of rubber products in this embodiment include tires, rubber tracks, and vibration-damping rubber, with tires being preferred. Among rubber products, tires are particularly effective in reducing environmental impact by reusing the aforementioned recycled carbon black due to their large production volume.

[0212] -tire-

[0213] When the rubber product of this embodiment is a tire, there are no particular limitations on the application site of the rubber composition in the tire, and it can be appropriately selected according to the purpose. Examples include the tread, tread base, sidewall, sidewall reinforcement rubber, and bead filler.

[0214] Conventional methods can be used as a tire manufacturing method. For example, components commonly used in tire manufacturing, such as a carcass layer, belt layer, and tread layer made of uncured rubber composition and / or cords, are sequentially stacked on a tire forming drum, and the drum is removed to obtain a green tire. The desired tire (e.g., a pneumatic tire) can then be manufactured by heating and curing the green tire in a conventional manner.

[0215] Example

[0216] The present disclosure will now be described in more detail with reference to embodiments, but the present disclosure is not limited in any way to the following embodiments.

[0217] (1) Analytical methods for the organic components and maximum DTG temperature of recycled carbon black

[0218] Using the trade name "STA7220" manufactured by Hitachi High-Technologies Corporation, the mass (m0) of the test recycled carbon black after heating to 120°C and holding for 1 hour and the mass (m1) after further heating to 550°C at 40°C / min and holding for 2 hours were measured by thermogravimetric analysis (TGA), and the organic composition of the test recycled carbon black was calculated according to the following formula:

[0219] Organic component (mass %) = (m0 - m1) / m0 × 100

[0220] In addition, the DTG value [μg / min] was determined, and the temperature at which the DTG value was maximized was used as the maximum DTG temperature (the temperature at which the DTA value was maximized in thermogravimetric analysis with the weight loss of organic components).

[0221] (2) Analytical methods for weight-average molecular weight (Mw) of liquid polymers

[0222] The weight-average molecular weight (Mw) of the liquid polymer, expressed as polystyrene, was determined by gel permeation chromatography (hereinafter sometimes referred to as GPC analysis; delivery unit: LC-20AB manufactured by Shimadzu Corporation; column: a combination of KF-803 and KF-804 manufactured by Showa Denko K.K. or a combination of G2000HXL and G4000HXL manufactured by Tosoh Corporation; detector: differential refractometer RID-10A manufactured by Shimadzu Corporation; analytical system: LabSolutions manufactured by Shimadzu Corporation; eluent: tetrahydrofuran), using monodisperse standard polystyrene as a reference. The measurement temperature was 40°C.

[0223] (Preparation of cross-linked rubber samples)

[0224] A rubber composition was prepared by compounding 50 parts by weight of carbon black [trade name "N330", manufactured by TokaiCarbon Co., Ltd.], 2.0 parts by weight of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 2.0 parts by weight of stearic acid, 2.25 parts by weight of zinc oxide, 0.6 parts by weight of vulcanization accelerator (N-cyclohexyl-2-benzothiazole sulfenamide), and 1.8 parts by weight of sulfur relative to 100 parts by weight of natural rubber. The rubber composition was then heated to crosslink the rubber composition to prepare a crosslinked rubber. The obtained crosslinked rubber was cut into 3mm × 3mm × 2mm shapes to prepare crosslinked rubber samples.

[0225] (Preparation of Recycled Carbon Black 1 - Metathesis)

[0226] 10 mL of tetrahydrofuran (THF) was added to 0.125 g of the above-mentioned crosslinked rubber sample, and the rubber was swollen by stirring at 25 °C for 24 hours. Next, 24 mg of Grubbs second-generation catalyst represented by the above structural formula (1-2) was added, and a metathesis reaction was carried out by stirring at 25 °C for another 24 hours. After the reaction, the reaction was stopped by adding 10 mL of methanol and 2.5 mL of ethyl vinyl ether. There was no residual rubber sample after the reaction, and the decomposition rate of the rubber sample was calculated as 100%. Subsequently, the solvent was distilled off under reduced pressure to obtain a mixture containing liquid polymer and recycled carbon black. The obtained mixture was centrifuged at 112,000 G for 60 minutes using a CP80NX (trade name, manufactured by Eppendorf Himac Technologies Co., Ltd.) to collect the recycled carbon black, and further, toluene solvent was added to the obtained recycled carbon black and centrifuged under the same conditions for washing.

[0227] The recycled carbon black after washing was analyzed by thermogravimetric analysis (TGA), and its organic content was found to be 9.8% by mass.

[0228] according to Figure 1 The relationship between temperature and DTG value [μg / min] shown is as follows: Figure 2 The relationship between temperature and DTG value (DTG / Maximum DTG[%]) is shown. The maximum DTG temperature when the DTG value is maximum is 370℃.

[0229] In addition, the weight-average molecular weight (Mw) of the liquid polymer obtained by centrifugation was analyzed and determined to be 11,000.

[0230] (Preparation of Regenerated Carbon Black 2 - Solvolysis)

[0231] In a reactor, 0.4 g of crosslinked rubber sample and 4 mL of toluene were added, and the mixture was stirred at 240 °C for 9 hours under an Ar atmosphere to carry out a decomposition reaction. After the reaction, the mixture was separated into a solvent (toluene) soluble component (mainly liquid polymer) and a solvent insoluble component (mainly carbon black).

[0232] The obtained solvent-insoluble fraction was centrifuged at 112,000 G for 60 minutes using a CP80NX (trade name, manufactured by Eppendorf Himac Technologies Co., Ltd.) to collect the regenerated carbon black. Further, toluene solvent was added to the obtained regenerated carbon black, and centrifugation was performed under the same conditions for washing. The washed regenerated carbon black was then vacuum dried at 50 °C for 12 hours.

[0233] The recycled carbon black after washing was analyzed by thermogravimetric analysis (TGA), and its organic content was found to be 11.9% by mass.

[0234] according to Figure 1 The relationship between temperature and DTG value [μg / min] shown is as follows: Figure 2 The relationship between temperature and DTG value (DTG / Maximum DTG[%]) is shown. The maximum DTG temperature when the DTG value is maximum is 390℃.

[0235] In addition, the weight-average molecular weight (Mw) of the liquid polymer obtained by centrifugation was analyzed and determined to be 28,000.

[0236] (Preparation and evaluation of rubber compositions)

[0237] The rubber composition was prepared according to the formulation shown in Table 1. In addition to the components shown in Table 1, the rubber composition was formulated with 2.0 parts by weight of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 2.0 parts by weight of stearic acid, 2.25 parts by weight of zinc oxide, 0.6 parts by weight of vulcanization accelerator (N-cyclohexyl-2-benzothiazole sulfenamide) and 1.8 parts by weight of sulfur, relative to 100 parts by weight of natural rubber (rubber component).

[0238] The tensile strength (TB) of the obtained rubber composition was measured using the following method.

[0239] (3) Measurement of tensile strength (TB)

[0240] The rubber composition is vulcanized to prepare vulcanized rubber test pieces. The test pieces are subjected to tensile testing according to JIS K 6251, and the tensile strength (TB) is measured.

[0241] [Table 1]

[0242]

[0243] *1 Unused carbon black: Trade name "N330", manufactured by Tokai Carbon Co., Ltd., organic content = 0.9% by mass, maximum DTG temperature = 333°C

[0244] *2 Commercially available recycled carbon black: Trade name "PB365", manufactured by Enrestec, organic content = 2.2% by mass, maximum DTG temperature = 315°C

[0245] *3 Recycled Carbon Black 1: Recycled carbon black obtained through metathesis, organic content = 9.8% by mass%, maximum DTG temperature = 370℃

[0246] *4 Recycled Carbon Black 2: Recycled carbon black obtained through solvent decomposition, organic component = 11.9% by mass%, maximum DTG temperature = 390℃

[0247] As can be seen from Table 1, the tensile strength (TB) of the rubber compositions of Examples 1 and 2, which are blended with recycled carbon black after washing with toluene according to the present disclosure, is comparable to the tensile strength (TB) of the rubber composition of Comparative Example 1, which is blended with unused carbon black.

[0248] On the other hand, it can be seen that the rubber composition of Comparative Example 2, in which commercially available recycled carbon black containing less than 5% by mass of residual organic components in the recycled carbon black after toluene washing is blended, has a significantly lower tensile strength (TB) compared to the rubber composition of Comparative Example 1, in which unused carbon black is blended.

[0249] Industrial availability

[0250] The recycled carbon black disclosed herein can be used in rubber products, such as tires, rubber tracks, and vibration-damping rubber.

Claims

1. A reclaimed carbon black obtained by decomposition of crosslinked rubber comprising diene rubber and carbon black, wherein the reclaimed carbon black has a residual organic component of 5 mass% or more after toluene washing.

2. The reclaimed carbon black according to claim 1, having a maximum DTG temperature of 350°C or more, wherein the maximum DTG temperature is a temperature at which a DTA value accompanying weight loss of the organic component is the largest in a thermogravimetric measurement.

3. A mixture of a reclaimed carbon black and a liquid polymer obtained by decomposition of crosslinked rubber comprising diene rubber and carbon black, wherein the reclaimed carbon black is the reclaimed carbon black according to claim 1, and the liquid polymer has a weight average molecular weight of 300,000 or less.

4. A mixture of a reclaimed carbon black and a liquid polymer obtained by decomposition of crosslinked rubber comprising diene rubber and carbon black, wherein the reclaimed carbon black is the reclaimed carbon black according to claim 1, and a proportion of a component having a molecular weight of 15,000 or less in the liquid polymer is 30 mass% or less.

5. A rubber composition comprising a rubber component and the reclaimed carbon black according to claim 1.

6. A rubber composition comprising a rubber component and the mixture of a reclaimed carbon black and a liquid polymer according to claim 3.

7. A rubber composition comprising a rubber component and the mixture of a reclaimed carbon black and a liquid polymer according to claim 4.

8. The rubber composition according to any one of claims 5 to 7, wherein the rubber composition is used for a tire.

9. A rubber article comprising a rubber member made of the rubber composition according to any one of claims 5 to 7.

10. The rubber article according to claim 9, wherein the rubber article is a tire. ​ ​ ​ ​ ​

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